1. Technical Field
Aspects of the invention relate to a so-called tandem type color image forming device, and in particular, relate to the image forming device provided with a sensor, which optically detects marks formed on a conveying member for a correction of a color registration error.
2. Related Art
Conventionally, a so-called color image forming device is configured such that, for correcting the color registration error, marks corresponding to the color components used for forming an image are formed on a conveying member (e.g., a sheet feed belt) and the positions of the marks are detected using a sensor. Specifically, the marks are detected such that a light source (e.g., an LED) is driven to emit light toward the conveying member and a photosensor (e.g., a photo-transistor) receives the light reflected by the conveying member on which the marks are formed.
In the image forming device of the above-described type, it is proposed that a shutter is provided between the conveying member and the photosensor to prevent a stain of the photosensor due to toner or some particles, which may be moved from the conveying member to the photosensor. In the image forming device employing the shutter as described above, it is also proposed that a status of the shutter, i.e., whether the shutter is opened or closed, should also be detected based on an amount of the light received with the photosensor. When the shutter does not open normally, the marks are not detected properly. Therefore, when the amount of the light the photosensor receives is extremely low, the image forming device judges that the shutter stays closed although the shutter is driven to open.